Canale L.C.F., Mesquita R.A., Totten G.E. Failure Analysis of Heat Treated Steel Components

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Effects due to Porosity

During the production of casting components,

the interactions between the liquid metal and

elements from the gaseous atmosphere, furnace

refractory, foundry ladle, molds, and core

materials are important factors from a techno-

logical and metallurgical point of view and are

responsible for desirable or undesirable changes

in the chem ical, physical, and mechani cal

properties of the metallic materials. The dim-

ensional precision grade of the feeding system

should also be taken into consideration.

Therefore, the quality of the casting product

is related to the physical integrity of the

component, that is, the absence or minimization

of the quantity of defects present. Among these

defects, the most important ones are those gen-

erated by the interaction of gas and metal that

promote the appearance of voids. In general,

there are two kinds of voids: those generated by

gas, and shrinkag e pores.

Porosity Caused by Gas

One of the factors that must be considered

in steel casting is the behavior of the gases in

the process. Generally, there are three major

sources that may contribute to porosity form-

ation (voids caused by gases) in steel castings.

These are:

 High initial gas content of the melt orig-

inating from the charge ingredients, melting

practice, or atmospheric humidity

 Reaction of carbon and dissolved oxygen

under certain melt conditions

 Mold-metal reactions between the evolved

mold and core gases at the solidifying cast-

ing surface

In addition, any combination of these three

sources may have an accumulative effect in

promoting porosity formation. However, the

gases normally held responsible for subsurface

porosity defects are nitrogen and hydrogen.

Types of Gas Porosity Defects. Pinholes

and blowholes are the two main kinds of por-

osity caused by the presence of gas (Ref 8).

Gas porosity (pinholes) refers to hydrogen,

oxygen, and nitrogen gases within a casting.

Molten metal has such an afﬁnity for H

, and

that it will disassociate it from other mol-

ecules, such as water or atmosphere gases, and

form a solution with it. As with most solutions,

as the temperature drops, these gases become

less soluble and precipitate as gas. The greater

the amount of gas in the molten metal and the

slower it solidiﬁes, the greater the gas voids. It

should be remembered that the H

comes from

the mold humidity, when the H

from the metal

is eliminated in the cleaning process performed

before pouring. These voids are generally

smooth, round, or slightly elongated and may be

somewhat localized in the areas of the casting

that solidify last. This type of porosity is gen-

erally undetectable visually, since the surface

of the casting solidiﬁes the quickest, preventing

the gases from forming holes large enough

to be visible on the surface, except through

Fig. 5

Crack in the bottom of a machine molded from AISI

1030 steel that happened in the normalization heat

treatment, caused by stress buildup in the sharp edge region

Fig. 6

Plastic injection mold casting in AISI H13 steel with

a crack from a sharp edge after a quenching heat

treatment

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ﬂuorescent-penetrant inspection or crack detec-

tion duri ng or after the heat treatme nt.

Gas holes (blowholes) are generally larger

and more localized voids than gas porosity, but

they retain the smooth, round, or slightly elon-

gated shape. They are usually caused by a

reaction in the mold medium, producing gas that

bubbles through the molten metal. The humidity

contained in the mold walls and cores is the main

source of the vapor that is necessary for defect

(gas bubble) formation in the casting compo-

nent. During mold ﬁlling, the gas generated by

the metal-mold reaction is eliminated to the

environment through permeability, a hole from

the exit of gases, and/or a rising gate. The resi-

dual quantity of gas that could lead to bubbles is

almost nonexistent or negligible. The exception

would be the use of low-permeable molds, for

example, the ones whose sand contains a high

percentage of ﬁnes, making the passage of the

gases to the environment difﬁcult. For the cores,

which may become completely surrounded by

liquid metal during mold ﬁlling, the problem can

be more serious. Gas elimination to the exterior,

including the gases gener ated by the binder and

collapsible materials, is extremely difﬁcult. It

may require the use of devices such as internal

wax wicks in all the core extensions, so the gases

are “sucked” toward the core prints and then

eliminated. A gas bubble can also occur, even

though it is not very common, as the result of an

inadequate measurement of the descent chan-

nels, distribution, and attack, which, during

pouring, can cause turbulence in the liquid metal

ﬂow or can cause air to be inhaled to the interior

of the mold cavity, where it mixes with the liquid

metal.

Behavior of Gases. Dissolved hydrogen and

nitrogen in the molten steel can cause a porosity

defect such as a pinhole. The extent of gas por-

osity depends on the amount of these gases, the

alloy, chemical kinetics, and the alloy surface

tension (Ref 9–12).

During solidiﬁcation of most steel alloys, the

component that is still liquid becomes more

concentrated in alloy elements due to its solu-

bility. This solubility difference is expressed by

the component ratio K

S/L

, which is a relation

between the quantity of solute present in the

solid and in the liquid. For most alloys, this value

is usually lower than 1, which indicates a liquid

enrichment during solidiﬁcation.

The hydrogen solubility in the austenite is

nearly 7 ppm, meaning that its solubility in the

molten and solid conditions is approximately the

same, and there is low hydrogen segregation

during the solidiﬁcation, which reinforces the

fact that the presence of gas bubbles caused by

hydrogen has other causes, for example, the

reaction with the moisture from the mold and/or

the cores (Ref 9).

For nitrogen, its component ratio for stable

and metastable eutectic solidiﬁcation is 1.9 and

2.2, respective ly (Ref 13). This shows that

nitrogen is less soluble in the liquid metal than in

the solid metal. However, it is good to highlight

that in a real situation, the solidiﬁcation involves

the liquid-solid diffusion and vice versa of a

larger quantity of elements, nitrogen being just

one of them. When nitroge n behavior in iron

alloys is analyzed, the most important element

whose mutual presence must be considered is

carbon. For example, in a 3.8% alloy at 1500



(2730



F), the nitrogen solubility at equilibrium

in the liquid metal is 110 ppm. At the time of

eutectic solidiﬁcation, this value is reduced

in the liquid to 97.5 ppm due to austenite en-

richment. In this sequence, because there is

an increase in the carbon percentage in the

liquid, the nitrogen solubility is reduced to

90 ppm. There is nitrogen saturation in the

liquid, and thus, this excess will cause the evo-

lution of the gas and may originate pinholes,

as seen in Fig. 7. When the possibility of pinhole

formation is evaluated, the component pressure

of all involved gases must be considered. When

this sum is higher than 1 atm, pinholes form.

So, in the previous example, the formation of

pinholes could happen with lower nitrogen

concentrations than those mentioned, needing

just the presence of other gases, such as hydro-

gen or oxygen, for example. It is also important

Fig. 7

Typical morphology of a defect called a pinhole,

caused by gases

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to consider the dynamic formation of these

bubbles in pinhole formation. However, the

thermodynamics of this event are very complex

and are not covered in this chapter.

How to Treat Pinhole and Blowhole Pro-

blems. In order to minimize or elim inate the

pinhole formation problem, a relatively simple

method can be used: bubbling argon in the

desulfurization reactor or ladle. When the argon

is blown into the bath, the gases in the atomic

form combine themselves on the bubble surface,

forming molecules from the respective gases

and H

). However, it is known that bubbling

is more effective in hydrogen elimination than in

nitrogen.

One of the most common alternatives to

reduce or eliminate blowholes is to increase

the pouring temperature. There will be a higher

ﬂuidity and time interval for the beginning of

component solidiﬁcation, giving time for the

gases to escape to the atmosphere. However,

care must be exercised in the decision to increase

the pouring temperature. The concentration

will also be bigger, and there is the risk of

the riser becoming undermeasured, thus allow-

ing the occurrence of a shrinkage cavity, in

addition to the possibility of a molding and core

system collapse, causing other defects in the

casting.

In summary, to minimize the effect of void

appearance from gases, the main measures to be

taken are:

 Control of the furnace atmosphere using

vacuum or gases with low solubility values

 Develop a project of feeding channels to

avoid turbulence

 Use sand molds and cores with the lowest

humidity and the maximum permeability

possible

 Use low-solubility gases that, when injected

in the liquid metal, carry the dissolved gases

to be eliminated to the surface

Porosity Caused by Shrinkage Pores

This type of porosity has a rough, irregular

shape. It is caused by a lack of adequate feed

metal during solidiﬁcation. This defect is an

internal void known as shrinkage pores. It

usually is detected only through ultrasonic or

radiographic tests or, during heat treatment,

when it cause s disruption in the components.

Shrinkage pores are not related to the high or low

presence of any kind of gases but to the feeding

system, directional solidiﬁcation, and pouring

temperature.

During the liquid-to-solid transformation,

there is a grouping of atoms that forms ordered

structures. In the majority of cases, this trans-

formation is followed by a density increase

(Fig. 8) and thus a shrinkage, because the metal

as a liquid occupies a larger volume than in the

solid state. The defect known as shrinkage pores

can be characterized as the appearance of non-

superﬁcial cavities in the casting component due

to the lack of predetermined and precise com-

pensation devices for the liquid metal shrinkage

that occurs during solidiﬁcation and/or the

metallic inserts for directional freezing.

If the concentration is a little higher than the

capacity of the system to compensate for it, or if

thicker pieces of the component work as risers

for thinner components, small, irregular voids

will be formed, as is seen in Fig. 9. However, if

the concentration is much higher than the com-

pensating mechanisms, there are large voids of

irregular shape s on the surface of the compo-

nent. These are called primary shrinkage cavi-

ties or simply shrinkage cavities, as seen in

Fig. 10, and are not discussed further in this

chapter.

In order to better understand shrinkage, an

example is given of the production of a cast iron

component with two kinds of molds: a nonstiff

mold with synthetic sand (green) and a stiff mold

with phenolic no-bake sand. In the one produced

with synthetic sand, there is a factor that must be

considered: the mold walls deform, increasing

the volume of the cavity when it receives the

liquid metal, and thus, it requires more metal to

Fig. 8 Density variation with temperature in metals

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compensate the increase in the volume. With the

rigid phenolic resin mold, there is no volume

increase in the cavity, and the additional liquid

metal is not necessary. On the contrary, when the

equivalent carbon is larger than 3.9%, there is a

graphitic expansion, which is larger than the

solidiﬁcation shrinkage and could cause a metal

reﬂux for the mold exterior.

Each metal or metal alloy presents a char-

acteristic concentration rate during the solidi-

ﬁcation process. Therefore, it is possible to

estimate quite precisely which feeding condition

will be necessary to avoid the occurrence of

porosity and shrinkage cavity problems. The

theoretical calculations to predict metal volume

shrinkage during the casting process are based

on a model proposed by Campbell (Ref 14),

using a sphere as an example.

There are basically three different types of

shrinkage that may occur during the solidiﬁ-

cation process, as shown in Fig. 11: liquid

shrinkage, solidiﬁcation shrinkage, and solid

shrinkage. During the casting process, the ﬁrst

type of shrinkage observed is the liquid one,

which happens with temperature decrease.

However, this does not represent signiﬁcant

problems in the quality of a casting component

when the volume reduction occur s linearly with

temperature decrease, and the necessary volume

of liquid material to compensate this volume

reduction can be given by risers.

On the other hand, the volume shrinkage that

occurs during solidiﬁcation of the liquid metal

can bring more serious problems to the casting

component, and thus, it requires more attention.

The major concern is to make the feeding pro-

cess, which replaces the liquid metal neces sary

to compensate the shrinkage in the system, very

precise in a way that allows for the attainment of

perfect components. This shrinkage compensa-

tion process determines the precision and per-

fection of the casting component and is inversely

(a)

(b)

Fig. 10

Primary shrinkage cavity forming large voids

of irregular shapes on the component surface.

(a) Schematic drawing. (b) Shrinkage cavity compensated for riser

Fig. 11

Schematic representation of the three regimens of

shrinkage: in the liquid state, during solidiﬁcation,

and in the solid state. Source: Ref 14

Fig. 9 Example of a shrinkage pore

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proportional to the quantity of shrinkage cavities

or shrinkage pores present in the obtained

component.

During the shrinkage p rocess that occurs in

the solid state, the component size starts to be

reduced. At this moment, the casting component

faces the resistance of the mold and/or core. This

kind of stress from the casting component, when

trying to contract, generates residual stresses

that may cause plastic deformation of the casting

component, hot tearing, or cracks during heat

treatment later on. Yet, this shrinkage depends

more on the volume reduction intrinsic to the

cast alloy and the project of the mold than on the

casting parameters.

Six Rules for Casting Component Feed-

ing. In the absence of gases and if the feeding of

liquid metal is appropriate, no porosity will be

found in the casting. However, because there are

many complex casting projects, there may be

regions of the mold with feeding problems,

allowing the internal hydrostatic tension in the

liquid metal to generate the conditions for the

formation of internal pores .

In the design of a component to be cast, it is

necessary to have an effective supply of material

in order to compensate the shrinkages pre-

viously mentioned. For the additional liquid

metal supplied to the system to compensate the

volume shrinkage that occurs during cooling, a

riser must be provided in the casting of the

component. The use of these risers, also known

as feeders, exothermic sleeves, or hot tops, can

eliminate the problem of shrinkage pores. The

quantity, form, and volume of these risers vary

according to the form and complexity of the

component to be cast. However, despite the fact

that there is a vast amount of literature on the

calculation and quantity of these risers, the

correct location of them depends on the experi-

ence of the process controller.

The following criteria, however, are con-

sidered fundamental for proper feeding of the

component, and thus, the defects caused by

shrinkage pores are reduced or eliminated:

 Thermal transfer criterion: The riser must

solidify at the same time or slower than the

casting.

 Volume criterion: The riser must contain

enough mass to fulﬁll the volume shrinkage

needs of the component.

However, there are still rules that are eventually

observed, and they deﬁne additional geometric,

thermal, and pressure criteria that are absolutely

necessary for perfect solidiﬁcation:

 The junction between the casting and the

riser must not create a hot spot. This place

cannot have a larger solidiﬁcation period

than the riser o r the casting component;

otherwise, it can cause the formation of a

shrinkage porosity.

 There must be a way in which the liquid

metal of the riser can reach all the required

regions.

 There must be a pressure variation in order to

cause a liquid material ﬂow in the right

direction.

 There must be enough pressure in all the

regions of the mold to avoid the formation

and growth of cavities.

Internal Porosity Formed from the Sur-

face. If ther e is not enough internal pressure

inside the component being cast and if the liquid

inside the mold is still connected with the liquid

in the external surface, it can be sucked to the

inside, causing the growth of porosities that are

connected with the surface (Fig. 12), because the

liquid naturally drags air with itself that stays in

the interdendritic spacings of the casting com-

ponent. This preforming mechanism is much

more common than imagined. It occurs mainly

in alloys with a very long cooling range, when

the development of the dendritic lattice means

that the aspiration of liquid in the neighboring

surfaces becomes easier than feeding from a

more distant point. The point at which the liquid

may be pulled from the surface can be anywhere

for an alloy with a long enough cooling period.

Thus, in an alloy with an intermediary solidiﬁ-

cation period, the starting point is usually a hot

spot, such as an internal corner or a recess angle

of the component.

The possibility of the connection of two

opposed surfaces in the same component

through the pores is one of the main reasons that

alloys with long solidiﬁcation times should not

be employed in the manufacturing of compo-

nents where high working pressures are applied,

such as hydraulic valves or motor cylinder

heads, because they would cause leakages. The

prerequisite in such com plex components is that

the interior should have positive pressure in all

points in order to avoid the connection of the

surfaces through internal porosities, which is

rarely achieved.

Internal Porosity from Nucleation. Alloys

with very short solidiﬁcation intervals, such as

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the aluminum, brass, and eutectic aluminum-

silicon alloys, do not present the connection

problem between the surface and pores because

they have a perfect solid layer in the ﬁrst stages

of solidiﬁcation, while the liquid feeding occurs

through the feeding channels. The internal

pressure decrease due to an inefﬁcient feeding at

the end of solidiﬁcation can create a pore

through nucleation in the interior of the liquid. In

this case, there is no connection with the external

surface of the casting.

So, in this kind of alloy, the porosity is usually

nucleated and is concentrated near the center of

the component. When it occurs in plates, for

example, it is referred to as axial porosity.

Unless subsequent machining operations pass

through the pores, the casting in such alloys is

tight.

After nucleation, the subsequent solidiﬁcation

provides the necessary driving force for pore

growth, which, if observed structurally, has

many similarities with the one started from the

surface.

Growth of the Shrinkage Pores. The ﬁrst

stage of shrink age pore growth is very fast.

According to Davies (Ref 15), this period should

be less than 60 ms. After this ﬁrst nucleation

stage, the growth of the pore happens more

slowly, being controlled by the heat extraction

rate of the mold. For the shrinkage pores that

started from the surface—the primary shrinkage

cavities, for example—there is not a fast ﬁrst

stage of nucleation. In fact, such a pore or

shrinkage cavity is simply formed as an answer

to the shrinkage of the solidiﬁcation.

During the solidiﬁcation of a casting compo-

nent, the liquid ﬂow from the reservoirs to the

areas that are being solidiﬁed make the level of

the reservoirs decrease. At the same time, there

is the advance of the solidiﬁcation front. Th is

joint action of decreasing the liquid level and the

advance of the solidiﬁcation front creates a conic

cavity, as shown in Fig. 13. This cavity is called

a primary shrinkage cavity in order to differ-

entiate it from a secondary shrinkage cavity,

which is porosity islands observed from long-

itudinal cuts guided according to a line from the

thinnest region of the primary shrinkage cavity.

In fact, these islands are interconnected in the

solid volume and are thus an extension of the

primary shrinkage cavity.

Example 1: Failure Analysis of a Mill

Gear with Defect Caused by a Shrinkage

Pore. The analyzed component corresponds to

a mill gear of 860 by 1900 mm (34 by 75 in.)

external diameter and 1050 mm and 15 teeth, as

shown in Fig. 14. The mill gear was purchased in

2003 and fractured in service during the 2003–

2004 harvest (only 3 months working). The aim

of this study was to verify the metallurgical

properties of the material and the causes that

eventually could have contributed to generate

the crack nucleation and the component fracture

after a short period of working.

Fig. 12 Internal porosity formed from the surface

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A chemical analysis of the studied component

was carried out by optical emission spectro-

scopy, and the results are shown in Table 1.

A tensile test was performed according to

ASTM E8M-98, an impact test accordi ng to

ASTM E23-91, and a hardness test according to

ASTM E0-96 (HBS 2.5/187.5/15). The results

are shown in Table 2.

The fracture, as can be observed, occurred

from the bottom of the tooth, propagating toward

the internal diameter. The visual aspect of the

cracked surface is an indication that the crack

occurred by nucleation and propagation of the

cracks through cyclic efforts (fatigue) of the uni-

directional type. The ﬁnal crack happened

after the longitudinal section had approximately

30% of its area taken over by cracks, as seen

in Fig. 15. The area of crack propagation by

fatigue indicates that there was propagation

during a relatively short period of the milling

operation. Most likely the component started

the operation already cracked, that is, with

casting defects of considerable dimensions near

the surface (subsuperﬁcial), causing the cracks

to arise and propa gate just at the beginning

of the harvest, which caused its fast milling

rupture.

Fig. 14 Aspects of the mill gear as received for analysis

Fig. 13 Primary and secondary shrinkage cavities

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Structural analyses were performed on sam-

ples from the fracture region and on the tooth

radio adjacent to the fractured region (Fig. 16,

17). It can be noted that the colony of subsurface

shrinkage cavities/porosity connected, which

probably caused the crack nucleation.

It could be concluded that the failure cause

was related to casting defects, such as connected

shrinkage cavities and porosity colonies, asso-

ciated with tensile loads applied during the mill

gear operation, which caused crack nucleation.

Figure 18 shows the crack starting point, proving

the failure cause.

Example 2: Failure Analysis of a Mill Gear

with Defect Caused by a Shrinkage Pore.

Figure 19 shows a sliced sample of the mill gear

with the tooth root used in the failure analysis.

Several mill gear presented had fractures on

several teeth roots after an intermittent load-

ing time. The chemical composition in weight

percent and the mechanical properties of the

steel in Fig. 19 are presented in Tables 3 and 4,

respectively, according to the data provided

by the manufac turer and compared to the

experimental ones. The phosphorus and sulfur

quantities are between the maximum limit

established by ASTM A148-93B, and the

quantity of other elements agreed with the

manufacturer speciﬁcation. The values obtained

for the yield strength (0.2%) and for tensile

strength agree with the expected ones.

The mill gear fractured through the mechan-

ism of crack propagation by fatigue. The cracks

nucleated from the casting defects, located

mainly in the third component of the width of the

mill gear and near the surface of the tooth root.

The low cooling rate during the solidiﬁcation

process is probably the main cause of the high

susceptibility to casting defect formation, such

as shrinkage pores. Inclusions and bubbles

represent a small component in the material

embrittlement, since they are too small com-

pared to shrinkage pores. Their presence should

be neglected.

Table 1 Chemical analysis of the studied material

Speciﬁcation

Composition, wt%

CSiMnP SCrNiMoCuAl

ASTM A148 Gr 105-85 0.270 0.477 0.859 0.023 0.017 0.946 1.774 0.242 0.058 0.073

Table 2 Properties of the studied material

Test

Speciﬁcation

ASTM A148 Gr 105-85

Tensile strength, MPa 804

Yield strength, MPa 679

Yielding at 50 mm, % 6.0

Reduction in area, % 10.0

Impact, J 30–35

Hardness, HB 257–259

Fig. 15

Aspect of the fracture surface showing that approxi-

mately 30% of the longitudinal section had been

taken over by the cracks diffused by fatigue. Many subsuperﬁcial

casting defects were also observed where the nucleation of the

cracks started.

Fig. 16

Structural analysis performed on samples from the

fractured region. Etched with 3% nital. Original

magniﬁcation: 100·

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Penetrating liquid analysis was performed on

the tooth root surface, and the result is presented

in Fig. 20. Localized cracks on the root center

have extended to the sides.

Figure 21(a) shows the observed micro-

structural aspect, where it is possible to note the

presence of several cracks in the sample interior.

These cracks were nucleated in several shrink-

age pores and have propagated by the fatigue

mechanism to the surface during cyclic loading.

The aspect of the fracture is mainl y transgra-

nular, which suggests that the material was not

embrittled by drawing back. Beyond the casting

defects, inclusions were observed in the sample,

some of them with sharp forms, as shown in

Fig. 21(b). It is important to note that thi s kind of

shape is undesirable since it is a potential crack-

nucleating site due to stress concentration. The

presence of sharp inclusions indicates that the

globalization process during casting was not

totally efﬁcient.

The proposed corrective actions include:

 Increase and standardize the extraction heat

rate from the casting mold in the region next

to the tooth root

 Improve the degassing process and impurity

control of the casting material

 Increase the thickness of the on-metal along

the region of the tooth root, with the goal of

increasing the probability of defect elim-

ination during the machining process

Effects due to Decarburization

during Microfusion

Among the several kinds of defects that may

occur during the cast ing process and that are

detected after heat treatment is the surface

Fig. 17

Structural analysis performed on samples from the

fractured region. Etched with 3% nital. Original

magniﬁcation: 200·

Fig. 18

Region adjacent to the fractured region showing a

transgranular crack generated in the casting process

and masked by material deformation during the radio machining

process, with propagation directed to the internal diameter

Fig. 19 Sample that was analyzed

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decarburization layer. It occurs in carbon steel

components cast by the lost-wax or microfusion

process. The identiﬁcation of this defect can

only be made after heat treatments in controlled

atmospheres; otherwise, this identiﬁcation is

impossible, since the decarburization can also

come from the heat treatment.

This decarburization results from the pre-

sence of atmospheric oxygen that remains in the

mold as a consequence of the inert feature of the

mold and its permeability in relation to the sur-

roundings. Some analyst s have measured the

thickness of the decarburized layer in carbon

steels cast by lost wax and discovered that it

increases proportionally to the temperature

increase in the mold and the volume/surface

ratio of the casting component (Ref 14).

Figure 22 shows a microfused decar burized

component that underwent heat treatment.

Effects due to Cold Joints

Cold joint is a kind of defect that happens in

cast components and normally has a signiﬁcant

effect on the structural integrity of the compo-

nent. This serious nonconformity happens when:

1) two portions of the metal, each coming from

different feeding/distribution canals of the mold,

meet and, instead of contributing to the form-

ation of a smooth and homogeneous surface,

provoke an undercut discontinuity called a cold

junction; 2) the solidiﬁcation process occurs too

far from the metal ﬂow coming from the feeding/

distribution place, where the liquid temperature

is lower than the necessary temperature; 3) the

pouring, feeding, and distribution channels are

underdimensioned and strangle the ﬂow of metal

necessary for the ﬁlling of the mold; and 4) the

molds have voids that need to be ﬁlled with such

Table 3 Chemical composition of the studied material

Source of data

Composition, wt%

CSiMnP S CrNiMoCuAlFe

Manufacturer 0.31 0.51 0.78 0.020 0.013 0.76 1.66 0.23 0.06 0.046 bal

Chemical analysis 0.31 0.50 0.80 0.018 0.017 0.76 1.66 0.24 ... ... bal

Table 4 Mechanical properties of the studied material

Source of data

Mechanical properties

, MPa s

, MPa e at 50 mm, % Reduction in area, % Hardness, HBW

Manufacturer 777.0 626.0 19.0 38.6 228

Experimental 780.1+16.2 606.7+15.3 10.2+1.9 35.9+14.1 230+4

Fig. 20

Cracks located in the tooth root revealed by the penetrating liquid technique. Detail of the central region with higher

magniﬁcation showing the machining imprints. The arrows show the extreme limits of the cracks.

Failures from the Casting Process / 163

Name ///sr-nova/Dclabs_wip/Failure_Analysis/5113_151-176.pdf/Chap_05/ 18/8/2008 3:11PM Plate # 0 pg 163